Traditional Béchamel Sauce

Ingredients 
4˝ cups of milk 
˝ cup of butter 
1/3 cup of plain flour 
1 stick of chopped celery 
1 peeled and diced carrot 
1 small diced onion 
grated nutmeg 
salt and pepper 
Method 
1 Heat the milk in the saucepan until near boiling. Remove from the stove and set to one side. 
2 In a separate saucepan, melt the butter and then add the chopped and diced vegetables. Cook until the onion has softened and is translucent in colour. 
3 Remove the pan from the heat and add the flour. Stir the mixture until a soft paste forms and then return to the heat. 
4 Cook for around 5 minutes, stirring frequently. 
5 Set the pan to one side and add the hot milk, a little at a time, whisking continuously. 
6 Return to the stove and bring to the boil, stirring constantly with a wooden spoon or a whisk. 
7 Season with the salt, pepper and nutmeg. 
8 Reduce the heat to low and simmer for 30 minutes, stirring from time to time. 
9 Remove the pan from the heat and strain the sauce through a sieve, so that only a white liquid remains. 
Serve as required.